1. Field of the Invention
The present invention relates to Schottky diodes, and more particularly, to Schottky diodes constructed for high reliability applications.
2. Description of Related Art
A Schottky diode comprises a semiconductor substrate and a metal contact layer deposited on the substrate to form a Schottky barrier at the metal-semiconductor interface. Typically, a separate metallization layer is insulatively disposed over the substrate to provide an electrical contact to the Schottky contact layer. Optionally, a separate diffusion barrier layer can be interposed between the metallization layer and the underlying Schottky contact layer to prevent interdiffusion of the metallization layer with the Schottky contact layer and the semiconductor substrate.
In high current applications, the Schottky contact layer may occupy a majority of the top surface of the semiconductor substrate. Current handling capacity can also be increased by connecting the external leads to the diode so that the current is directed vertically through the semiconductor substrate. For example, if one external lead is electrically connected to the top metallization layer and a second external lead is connected to a metallization layer on the bottom surface of the substrate, current will flow generally vertically through the device.
In some applications, it is important for the diode assembly including the leads to the Schottky diode to be able to withstand a variety of mechanical forces including vibration, torsion, compression, stresses due to temperature shock and temperature cycling, etc., while maintaining good electrical contact to the Schottky diode. Often, the bottom lead is metallurgically bonded to the bottom metallization layer. Metallurgical bonding can provide a very strong mechanical connection as well as good electrical and heat conduction to the diode. However, because of the proximity of the Schottky contact layer to the top metallization layer, the top external lead has not generally been metallurgically bonded to the top metallization layer. Known Schottky diodes are not believed to be able to withstand metallurgical bonding of the top lead without destruction or serious degradation of the Schottky contact layer.
In some prior designs, the top lead is mechanically compressed against the top metallization layer. For example, after bonding the bottom lead to the bottom of the substrate, the top lead is abutted against the top metallization layer of the diode. The Schottky diode and the ends of the top and bottom leads are then encased in a glass sleeve which is subsequently heated and shrunk providing a strong contact pressure between the top lead and the top metallization layer of the diode. This pressure contact between the top lead and the top metallization layer of the diode is often not as strong or reliable as a metallurgical bond.